Patient-specific spinal fusion cage and methods of making same

ABSTRACT

A method of determining disc space geometry with the use of an expandable trial having endplate-mapping capabilities. An expandable trial is inserted into the disc space and its height is adjusted to obtain the desired decompression and spinal alignment (which is typically confirmed with the use of CT or Fluoroscopic imaging). The endplate dome/geometry dome is then determined by one of the following three methods:
         a) direct imaging through the trial,   b) balloon moldings filled with flowable in-situ fluid (for example, silicon, polyurethane, or PMMA) from superior/inferior endplates or   c) light-based imaging through superior &amp; inferior balloons.

BACKGROUND OF THE INVENTION

Spinal fusion cage subsidence and expulsion are frequently issues ofconcern in spinal fusion surgeries. Restenosis due to subsidence hasbeen often documented. See, for example, Marchi et al., J NeurosurgSpine 19, 110-118, 2013. Four subsidence grades have been developed andshown to correlate with the likelihood of restenosis and associatedrevision rates. The significant potential of endplate-conformingimplants in reducing the likelihood of subsidence has also beenconsidered. See, for example, de Beer et. al., Spine Journal 12,1060-1066, 2012.

Insufficient contact area and load transfer between the vertebral bodyand the cage can produce excessive load transfer in specific locationsthat can lead the cage to settle or subside into the vertebral body.Insufficient contact area or pressure differentials between the cage andthe vertebral bodies can also produce micro-motions and/or macro-motionsthat can increase subsidence and result in cage expulsion from the discspace. It is believed that this insufficient contact area is in part dueto the anatomical variability in the curvature of the endplates fromlevel to level and patient to patient. Additionally, low bone mineraldensity index or overaggressive decortications of the endplate canreduce the strength of the endplate and the ability to transfer loadfrom vertebral body to vertebral body.

To minimize these risks, surgeons carefully prepare the opposingvertebral endplates and typically insert the cage having as large afootprint as possible in order to maximize the contact area. Whenappropriate, the surgeon also places the cage on the apophyseal rings toprovide as much support and load transfer as possible for spinaldistraction while ensuring the cage is securely nested within the discspace.

These concerns have also been addressed by modifying the shape of theintervertebral cage. Although some cages have been domed to increasecontact area, these are often unable to fit and conform to each discspace due to inherent human anatomical variability.

Other procedures concern the use of preoperative CT- or MRI-derived datato facilitate the manufacturing of patient-specific spinal devices. Asignificant limitation with these devices and patents is that theyassume the correct disc space geometry can be clearly identified priorto surgical intervention for disc space released, FSU decompression andspinal alignment corrections. Additionally, the state of the art doesnot include patient-specific intra-operatively fabricated cages norpatient-specific intra-operatively assembled cages.

U.S. Pat. No. 5,514,180 (Heggeness) discloses intervertebral deviceshaving fixed shapes for accommodating the defined surface contours ofvertebral endplates. A method for quantitatively determining thethree-dimensional morphology of vertebral surfaces, particularlyvertebral endplates, is also disclosed.

SUMMARY OF THE INVENTION

The present invention relates to the intra-operative determination of adesired cage footprint, height, lordosis, 3D geometry and endplatecontact area, once spinal disc space intervention and decompression havebeen achieved and spinal alignment has been determined. The presentinvention provides certain patient-specific spinal fusion cages as wellas the method of determination, fabrication and implantation of thesepatient-specific spinal fusion devices. This method and devices allowfor the intra-operative determination, fabrication and implantation ofcustom, patient-specific implants to maximize contact area between theprepared endplates and the fusion cage with the objective of reducingsubsidence and expulsion.

In one embodiment of the present invention, there is provided a methodof determining disc space geometry with the use of an expandable trialhaving endplate-mapping capabilities. In one preferred embodiment, anexpandable trial is inserted into the disc space and its height is thenadjusted to obtain the desired decompression and spinal alignment (whichis typically confirmed with the use of CT- or fluoroscopic imaging). Thegeometry of the dome (i.e., the cavity between the trial and theendplates) is then determined by one of the following three methods:

-   -   a) direct light or ultrasound imaging through the trial,    -   b) balloon moldings filled with a flowable, in-situ fluid (for        example, thermosets such as silicone, polyurethane, or an        acrylic polymer such as PMMA, or thermoplastics) attached to        superior/inferior prosthetic endplates or    -   c) light absorption imaging through superior & inferior balloons        attached to superior/inferior prosthetic endplates.

Therefore, in accordance with the present invention, there is providedan intervertebral trial having a distal end portion having upper andlower surfaces defining a height therebetween, wherein the height isadjustable and is adapted for insertion into a disc space betweenopposing vertebral endplates, and wherein the distal end portion has afunctional feature adapted to map a contour of a vertebral endplate.

Also in accordance with the present invention, there is provided amethod of imaging an contour of a vertebral endplate, comprising thesteps of;

-   -   a) selecting the trial described above,    -   b) inserting the trial into the disc space,    -   c) expanding the height of the trial to create a first cavity        between the upper surface of the trial and the upper vertebral        endplate, and    -   d) producing an electronic 3D image of the first cavity.

Also in accordance with the present invention, there is provided amethod of manufacturing a patient-specific intravetebral implant for apatient having a disc space defined by a pair of opposed vertebralendplates, comprising the steps of:

-   -   a) intraoperatively obtaining a 3D image of each of the        vertebral endplates,    -   b) intraoperatively manufacturing, from the 3D images, the        patient-specific intervertebral implant, and    -   c) inserting the patient-specific intervertebral implant into        the disc space in the patient.

Also in accordance with the present invention, there is provided amethod of building a patient specific intravertebral implant for apatient having a disc space defined by a pair of opposed vertebralendplates, comprising the steps of:

-   -   a) intraoperatively obtaining a 3D image of each of the        endplates,    -   b) intraoperatively manufacturing, from the 3D images, a pair of        prosthetic endplates,    -   c) intraoperatively attaching each prosthetic endplate to a core        component to produce an assembled, patient specific        intravertebral implant.    -   d) inserting the assembled patient specific intravertebral        implant into a disc space in the patient.

Also in accordance with the present invention, there is provided apatient-specific intervertebral fusion cage for insertion into a discspace defined by opposing upper and lower vertebral endplates in apatient, comprising:

-   -   a) an intermediate modular core component having an upper        surface and a lower surface,    -   b) an upper endplate attached to the upper surface of the core        component,    -   c) a lower endplate attached to the lower surface of the core        component, wherein each of the upper and lower endplates are        manufactured from 3D images of the opposing upper and lower        vertebral endplates of the patient.

DESCRIPTION OF THE FIGURES

FIGS. 1A-1B disclose front and side views of a direct imaging embodimentof the present invention.

FIG. 2A-2B disclose front and side views of a light imaging embodimentof the present invention using graduated balloons.

FIGS. 3A-3F disclose embodiments of the balloon molding embodiment ofthe present invention.

FIG. 4 discloses a perspective view of a milling machine used to makethe endplates of the present invention.

FIGS. 5A-5G disclose a rapid prototyping-based embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the trial of the present invention comprises the aforesaiddistal portion, a proximal end portion comprising a handle, and anelongated intermediate portion. Preferably, the elongated intermediateportion comprises a rod. Also preferably, the upper and lower surfacesare substantially planar.

In one embodiment of the invention, the imaging feature comprises anendoscope having a light emitter, such as a fiber optic. In thisembodiment, the light emitter emits light waves into the cavity betweenthe trial and the vertebral endplate to create return signals. Amonitoring system including a camera creates a 3D image of the cavityfrom the return signals. A screen may also provide a visualidentification of the endplate contour.

In one embodiment, the fiber optic emits light waves from a tip of afiber optic into the cavity between the vertebral endplate and thetrial. Light waves are emitted at frequencies sufficient to imageendplate contours. In this embodiment, the fiber optic emits light wavesin a direction normal to the upper or lower surface of the trial. Lightwaves are continuously emitted and contact a vertebral endplate as thecamera traverses the upper surface of the trial. In alternativeembodiments, fiber optic emits light waves intermittently. The lightwaves return, and the signals from the returning light waves arecollected by the camera and transmitted to a signal receiver. Themonitoring system uses the signals received by the signal receiver tocreate a 3D image of the vertebral endplate contour. The signal receiverincludes any device suitable for receiving a light signal. The signalreceiver may be located at any suitable location. In one embodiment, thesignal receiver is located in proximity to the patient upon which theendoscope is being used. For instance, in an embodiment, the signalreceiver is located in the operating room with the patient. Themonitoring system comprises any devices and methods suitable forproviding a 3D image from signals created by light waves contactinginternal body structures. In an embodiment, the monitoring systemcomprises a camera. The camera includes any device suitable forphotography, wherein photography refers to diagnostic imaging in whichlight is used to image internal body structures. The monitoring systemmay be located at any suitable location. In an embodiment, themonitoring system is located in proximity to the patient upon which theendoscope is being used. For instance, in an embodiment, the monitoringsystem is located in the operating room with the patient. The monitoringsystem may also include a light imaging screen. The light imaging screenincludes any screen suitable for displaying the image of internal bodystructures such as the vertebral endplate. In an embodiment, themonitoring system comprises the signal receiver.

In one embodiment, the monitoring system allows for the distance fromlight emitter to the vertebral endplate to be determined, visualized ona viewing screen, and aggregated into a 3D image of the cavity. Thedistance may be determined by any suitable distance determinationtechniques used with monitoring systems.

In one embodiment, the camera is a wireless camera. A wireless cameramay be powered by any suitable power source such as battery power,magnetic induction resonance, and the like. Any magnetic inductionresonance method suitable for use with a surgical camera may be used. Inone embodiment, the camera is powered through magnetic inductionresonance between an ex vivo source and a receiver. In one embodiment,the receiver is contained within or alternatively on the camera.

In one embodiment, this 3D image created from light signals is then usedto create a patient-specific intervertebral implant. In one embodimentthereof, this 3D image is then used to create a patient-specificendplate that can be attached to a modular core component of anintervertebral implant.

In one embodiment of the invention, the imaging feature comprises anultrasound emitter, or transducer. In this embodiment, the ultrasoundtransducer emits sound waves into the cavity between the trial and thevertebral endplate to create return signals. The monitoring systemincludes an ultrasound imaging device that creates a 3D image of thecavity from the return signals. An ultrasound imaging screen may alsoprovide a visual identification of the endplate contour.

In one embodiment, the ultrasound transducer emits sound waves from atip into the cavity between the endplate and the trial. Sound waves areemitted at frequencies sufficient to image endplate contours. In oneembodiment, the transducer emits sound waves in a direction normal tothe upper surface of the trial. In some embodiments, sound waves arecontinuously emitted and contact a vertebral endplate as the transducertraverses the upper or lower surface of the trial. In alternativeembodiments, transducer emits sounds waves intermittently. The soundwaves return, and the signals from the returning sound waves arecollected by the transducer and transmitted to a signal receiver. Amonitoring system uses the signals received by the signal receiver tocreate a 3D image of the cavity between the vertebral endplate and thetrial. The signal receiver includes any device suitable for receiving asignal from an ultrasound transducer. The signal receiver may be locatedat any suitable location. In an embodiment, the signal receiver islocated in proximity to the patient upon which ultrasound transducer isbeing used. For instance, in an embodiment, the signal receiver islocated in the operating room with the patient. The monitoring systemcomprises any devices and methods suitable for providing a 3D image fromsignals created by sound waves contacting internal body structures. Inan embodiment, the monitoring system comprises an ultrasound device. Theultrasound device includes any device suitable for ultrasonography. Itis to be understood that ultrasonography refers to diagnostic imaging inwhich ultrasound is used to image internal body structures. Themonitoring system may be located at any suitable location. In anembodiment, the monitoring system is located in proximity to the patientupon which the transducer is being used. For instance, in an embodiment,the monitoring system is located in the operating room with the patient.The monitoring system may also include an ultrasound imaging screen.Ultrasound imaging screen includes any screen suitable for displayingthe image of internal body structures such as the vertebral endplate. Inan embodiment, the monitoring system comprises the signal receiver.

In one embodiment, the monitoring system allows for the distance fromultrasound transducer to the vertebral endplate to be determined,visualized on ultrasound imaging screen, and aggregated into a 3D imageof the cavity. The distance may be determined by any suitable distancedetermination techniques used with monitoring systems such as ultrasounddevices.

In one embodiment, the transducer is a wireless transducer. A wirelesstransducer may be powered by any suitable power source such as batterypower, magnetic induction resonance, and the like. In one embodiment,ultrasound transducer is powered through magnetic induction resonancebetween an ex vivo source and a receiver. In one embodiment, thereceiver is contained within or alternatively on the transducer.

In one embodiment, this 3D image created from ultrasound signals is thenused to create a patient-specific intervertebral implant. In oneembodiment thereof, this 3D image is then used to create apatient-specific endplate that can be attached to a modular corecomponent of an intervertebral implant.

In some embodiments, and now referring to FIGS. 1A and 1B, there isprovided a trial comprising:

-   -   a) an expandable core component 1 (here shown as a pair of        pivoting arms),    -   b) an upper plate 3 and a lower plate 5, each plate pivotally        attached to the core component, and    -   c) upper 7 and lower 9 cameras located between the core        component and the respective plates.

The plates are preferably transparent to light. The core and platecomponents are first advanced into the disc space and the core is thenexpanded, so that the plates contact the periphery of the opposedvertebral endplates. Next, the cameras are advanced into the disc spaceas they emit light (shown as a dotted line) and record images of theupper and lower cavities. These images are then aggregated to produce a3D image of each cavity.

In one embodiment, the 3D images of the cavities between the trial andthe opposed vertebral endplates are provided by balloon moldings. Inthis embodiment, and now referring to FIGS. 3A-3B, an elastic,conformable, deflated balloon is attached to one of the upper and lowersurfaces of the trial, and a distal end portion 23 of a tube 25 isconnected to the opening of the balloon via a throughhole 27 in theplates. Once the trial is expanded to contact the periphery of thevertebral endplate, a curable fluid is delivered through the tube intothe balloon to expand the balloon 21 so that it conforms to the contourof the vertebral endplate. The delivery of the fluid can be halted whena known pressure is obtained. The fluid then cures to a solid resin inthe shape of a dome. FIG. 3C shows a perspective view of aballoon-molding trial of the present invention, including the expandingcore 31, upper 33 and lower 35 surfaces, and conforming balloons 37. Thetrial may also have a graft window 41. Next, the expanded trial isretracted so that the cured molding 30 (whose cross sections are shownin FIG. 3D-3E) may be removed from the disc space. In one embodiment,this molding is then used to create a patient-specific intervertebralimplant. In one embodiment thereof, this molding is then used to createa patient-specific endplate that can be attached to a modular corecomponent 42 (whose cross-section is shown in FIG. 3F) of anintervertebral implant. In another, this molding is then used to createan entire patient-specific implant. In another, this molding is thenused as a template to a machine-finished implant.

In one embodiment, the image feature is adapted from the Lantos AURA™technology. This technology is described in US2013-0002426; U.S. Pat.No. 8,384,916; US2014-0002613; and U.S. Pat. No. 8,619,154, thespecifications of which are hereby incorporated by reference in theirentireties. In this embodiment, an elastic, deflated balloon is attachedto one of the upper and lower surfaces of the trial, and a distal end ofa tube is connected to the opening of the balloon. Once the trial isexpanded to contact the periphery of the vertebral endplate, a fluid isdelivered into the balloon to expand the balloon so that it conforms tothe contour of the vertebral endplate. The delivery of the fluid ishalted when a known pressure is obtained. The trial has two lightemitters that emit two different wavelength bands of fluorescent light.The trial also has light receivers that register the absorption of thetwo different lights as they travel through an absorbing mediumcontained within the balloon. Related imaging technology then capturesthe images and uses algorithms to combine the images into a full 3D scanof the cavity. This embodiment

may also be adapted to use the graduated balloon technology discussedabove.

In one embodiment, this 3D image created from these light signals isthen used to create a patient-specific intervertebral implant. In oneembodiment thereof, this 3D image is then used to create apatient-specific endplate that can be attached to a modular corecomponent of an intervertebral implant.

In some embodiments, the core, plate and balloon components are firstadvanced into the disc space and the core is then expanded, so that theplates contact the periphery of the opposed vertebral endplates. Next,the elastic balloons are inflated to conform to the contour of theopposed endplates. Next, the cameras are advanced into the disc space(or retracted from the disc space) as they emit light and record imagesof the balloons as they conform to the upper and lower cavities. Theknown distance and spacing of the markings on the graduated balloonsallow for imaging and determination of the expanded 3D geometry.

In some embodiments, and now referring to FIGS. 2A and 2B, there isprovided a trial comprising:

-   -   a) an expandable core component 11 (here shown as a pair of        pivoting arms),    -   b) an upper plate 13 and a lower plate 15, each plate pivotally        attached to the core component, and    -   c) upper 17 and lower 19 graduated balloons attached to the        respective plates.

Modular endplates can be milled or machined from blank stock in theoperating room based upon information of the 3D geometry of the cavityusing known, computer-based rapid prototyping techniques, such as SLA,fusion deposition modeling, selective metal sintering and selectivelaser sintering. The geometry can be obtained directly from the 3Dimaging, directly from the moldings, or by reconstructing of the 3Dimages obtained from the two or more balloons. This geometry informationcan be transferred to a milling machine in the form of millinginstructions. The endplates can also be 3D-printed by, for example,stereolithography in the operating room. The endplates can also beassembled from modular components which are indicative of typicalendplate geometries to create the patient specific devices with enhancedcontact area.

In one milling manufacturing embodiment, and now referring to FIG. 4,there is provided an apparatus 51 suitable for manufacturing implants ofthe present invention. The apparatus has a base 53, a 3D-moveableforming device 55 having replaceable cutting tips 57, a shield 59, areadout 61, an input 63 for receiving milling instructions, a built inbluetooth connection (not shown), and a multifunction knob interface 67.The cutting tips work upon a blank to yield a finished endplate cut tomatch a patient's specific anatomy.

In one stereolithography manufacturing embodiment, and now referring toFIG. 5A, a 3D printer has a light emitter 71 situated above a pool 73 ofcurable resin. The 3D printer receives printing instructions suitablefor producing an endplate of the present invention. In accordance withthose instructions, the light emitter emits a beam of light onto thepool surface in a pattern indicative of the endplate to be manufactured.The light causes a chemical reaction to occur in the upper layer of thepool so as to cure that layer and thereby build a layer 75 of theendplate. By retracting scaffold 79, the cured endplate layer is thensubmerged to expose a new layer of uncured resin at the top of the pool.The process then repeats itself to produce a second cured layer of theendplate, and so on until the entire endplate is produced. The pairedendplates so produced, shown in FIGS. 5B-5D, can be provided in smalldome 81 (FIG. 5B), medium dome 83 (FIG. 5C) and large dome 85 (FIG. 5D)varieties. These endplates may further be fabricated with dovetailgrooves 87, for easy assembly to cores that may be furnished in small 91(FIG. 5E, medium 93 (FIG. 5F) and large 95 (FIG. 5G) sizes. These coreshave matching dovetails 97.

Once the endplates are assembled to the modular core, or once the fulldevice is fabricated, they or it may be inserted into a disc space byany known means. In some instances, to avoid impaction of a cage withthe endplate dome which is frequently larger than the disc space entrypoint, the components of the implant may be serially inserted into thespace, whereby the upper and lower endplates are first inserted into thedisc space, and then the central core spacer is inserted therebetween toobtain the final implant.

We claim:
 1. A method of treating a patient comprising the steps of; a)selecting an intervertebral trial having a distal end portion havingupper and lower surfaces defining a height therebetween, wherein theheight is adjustable and is adapted for insertion into a disc spacebetween opposing vertebral endplates, and wherein the distal end portionhas a functional feature adapted to map a contour of a vertebralendplate, b) inserting the trial into the disc space, c) expanding theheight of the trial to create a first cavity between the upper surfaceof the trial and the upper vertebral endplate, and d) producing anelectronic 3D image of the first cavity by first rendering a balloonmolding of the first cavity and then carrying out light absorptionimaging of the balloon molding, e) intraoperatively manufacturing, fromthe 3D image, a patient-specific intervertebral implant, and f)inserting the patient-specific intervertebral implant into the discspace in the patient.
 2. The method of claim 1 wherein the expansionstep creates a second cavity between the lower surface of the trial andthe lower vertebral endplate.
 3. The method of claim 2 furthercomprising the step of: g) producing a 3D image of the second cavity.